1. Field of the Invention
The present invention relates to a substrate heating apparatus and semiconductor fabrication method used in a semiconductor substrate heating process.
2. Description of the Related Art
Annealing for processing a semiconductor substrate at a high temperature has been conventionally extensively used. For example, a process of activating an ion-implanted impurity and a rapid thermal process (rapid thermal anneal) for, for example, recovering crystal defects caused by ion implantation are widely performed.
When a silicon carbide (SiC) substrate is used, for example, the material characteristics suppress thermal diffusion, and local dopant control uses ion implantation. However, SiC crystals sometimes break when implanting impurity ions accelerated by high energy. A high-temperature heating process is performed to electrically activate the implanted impurity by recrystallizing the almost amorphousized sic.
This substrate heating process is performed by a semiconductor fabrication apparatus, or performed in a semiconductor fabrication step by a substrate heating apparatus which includes a heating means for heating a substrate placed in a process chamber that can be evacuated, and heats a substrate placed in the process chamber by the heating means.
For example, an apparatus denoted by reference numeral 100 in FIG. 1 is conventionally known as the substrate heating apparatus. In the substrate heating apparatus 100, a heating means 104 installed in a suscepter 102 in a process chamber 101 that can be evacuated by an evacuating means (not shown) heats a substrate 103 placed on the suscepter 102.
As the heating means 104, a high-frequency induction heating means, a thermal electron generating means for electron bombardment heating, an infrared lamp, or the like is used.
The heating process of a semiconductor substrate, particularly, the heating process of an SiC substrate is performed at a high temperature of about 1,500° C. to 2,000° C.
In this substrate heating process, the substrate heating apparatus 100 as shown in FIG. 1 cannot evenly heat the substrate 103 very well.
Accordingly, a substrate heating apparatus 110 as shown in FIGS. 2A and 2B has been proposed (International Publication WO2006/043530).
The substrate heating apparatus 110 includes a heating means 104 for heating a substrate 103 placed in a process chamber 101 that can be evacuated, and heats the substrate 103 placed in the process chamber 101 by the heating means 104. In the embodiment shown in FIGS. 2A and 2B, a suscepter 102 is installed between the heating means 104 and substrate 103. The basic structure and form are the same as those of the substrate heating apparatus 100 shown in FIG. 1.
The difference of the substrate heating apparatus 110 shown in FIGS. 2A and 2B from the substrate heating apparatus 100 shown in FIG. 1 is that a heat receiving member for receiving the heat from the heating means 104 via the suscepter 102 is installed to oppose the suscepter 102 with the substrate 103 being sandwiched between them.
In the embodiment shown in FIGS. 2A and 2B, this heat receiving member is a cap 107 that covers the substrate 103 from above the suscepter 102, thereby isolating the substrate 103 from a space 113b in the process chamber 101.
The heat receiving member such as the cap 107 that receives the heat from the heating means 104 via the suscepter 102 is installed to oppose the suscepter 102 with the substrate 103 being sandwiched between them. The substrate heating apparatus 110 shown in FIGS. 2A and 2B can achieve the remarkable effect of evenly heating the substrate 103 because the substrate 103 is placed in a closed space 113a formed by the suscepter 102 and cap 107.
Although the conventional substrate heating apparatus 110 shown in FIGS. 2A and 2B can achieve the notable effect of evenly heating the substrate 103, surface roughness sometimes occurs on the substrate 103 when a semiconductor substrate such as an SiC substrate is heated at a high temperature of about 1,500° C. to 2,000° C.
When this SiC substrate having a roughened surface is used in a MOSFET (MOS Field Effect Transistor), the channel mobility in the MOSFET decreases.
That is, when forming a MOSFET or the like by using an SiC substrate having a roughened surface, a gate insulating film and the like are formed on the roughened surface of the SiC substrate, so no good interface can be obtained. As a consequence, the performance as a transistor deteriorates. Also, even when simply forming a contact with a metal, the contact resistance may rise if the metal is brought into contact with the roughened surface.
A gas discharged from the surfaces of the suscepter 102 and cap 107 presumably has influence on the surface roughness that occurs when a semiconductor substrate such as an SiC substrate is heated at a high temperature.
Accordingly, it is proposed to form coatings 108 and 109 made of a material that discharges no gas during the substrate heating process, on that surface of the suscepter 102 installed between the heating means 104 and substrate 103, on which the substrate 103 is placed, and on that surface of the cap 107 as the heat receiving member, which faces the substrate 103. The coatings 108 and 109 suppress the surface roughness of the substrate 103 caused by the gas discharged from the suscepter 102 and cap 107 during the substrate heating process.
It is possible to achieve the remarkable effects of evenly heating the substrate 103 and suppressing the surface roughness by installing the heat receiving member such as the cap 107 that receives the heat from the heating means 104 via the suscepter 102, so as to oppose the suscepter 102 with the substrate 103 being sandwiched between them, and by forming the coatings 108 and 109 made of a material that discharges no gas during the substrate heating process, on that surface of the suscepter 102 on which the substrate 103 is placed, and on that surface of the cap 107 which faces the substrate 103.
Even when the coatings 108 and 109 are formed, however, it is difficult to completely eliminate the problem that the surface roughness occurs on the substrate 103 during the heating process. Therefore, the present inventor made extensive studies to heat a substrate more evenly and eliminate the surface roughness more reliably.
Consequently, the present inventor has found that even when the coatings 108 and 109 made of a material that discharges no gas during the substrate heating process are formed to suppress the discharge of a gas from the suscepter 102 and cap 107, the cap 107 or the like may discharge a gas through an incompletely coated portion or fine pinhole. The present inventor has also found that the cap 107 or the like may discharge a gas due to the grain boundaries formed during the heating process performed at a high temperature of about 1,500° C. to 2,000° C.